The importance of backspin retarders in pumps, particularly progressing cavity pump drives, is well known in the art. Backspin is a condition which occurs when a well head is being shut down or restarted. Progressing cavity pumps are located at the bottom of an oil well bore, which in some cases, may be several thousand feet deep. Thus, pumping oil to the surface requires very high pressure. In addition, the pump drive rods, called sucker rods, may be wound torsionally several dozen times. When the pump is stopped, the combination of the very high pressures or head above the pump and sucker rod wind-up cause the pump and drive mechanism to rotate in reverse. If not controlled, the drive can rotate at speeds high enough to cause drive sheaves and other components mounted in the top drive to fly apart and cause serious injury to service personnel at the surface.
Thus, backspin retarders have been developed to control backspin until the fluid head and sucker rod wind-up have been reduced to safe levels. Existing backspin retarders have met with varying degrees of success. Typical prior art of retarders use built-in pumps to discharge fluid through an orifice and cause increased braking as speed increases. Some retarders have been placed on drive motor shafts. However, if a drive belt breaks, backspin protection is lost completely. Generally, prior art retarders have not been as reliable and durable as is desired considering safety issues.